This invention relates to an electronic control unit of the type having a housing unit and a stamped sheet metal part for a strip conductor, with electric components arranged thereon, and to a process for manufacturing such a control unit.
A control unit of this type and a process for manufacturing it are disclosed in German patent document DE 44 04 986 A1. There, the strip conductor structure is fastened on a carrier, and thereafter electronic components are bonded with it. At the application site (in this case, an electric motor controlled by the control unit), the carrier is provided with a cover, so that the strip conductor structure and the components are sheathed by a housing.
The manufacturing of this known control unit requires high expenditures. It also has a low mechanical stability because, for example, the housing offers protection against only moisture or dirt, and does not increase the mechanical stability of the control unit, which is determined essentially by the stability of the carrier.
It is an object of the present invention to provide an electronic control unit of the initially mentioned type which has a high mechanical stability, and can be manufactured in a particularly simple fashion.
This object is achieved by the control unit according to the invention, which has a housing produced by means of injection molding, resulting in a compact construction that is largely unsusceptible to mechanical as well as thermal and atmospheric influences. The manufacturing takes place by means of the injection molding technique known from integrated circuits which are easy to handle and which have a high degree of maturity. The mechanical and thermal characteristics of the control unit can be optimally adapted to satisfy applicable requirements, as a function of the plastic material which is used and/or the applied manufacturing process.
According to one embodiment of the invention, additional structural strip conductor sections are used, so that sensitive components, which would be damaged during the manufacturing of the housing, can be moved to the outside, and can later be fastened to the control unit. This arrangement permits further adaptation of the plastics-related technique to the required mechanical characteristics of the housing, because the loading capacity of the other electric components arranged in the housing no longer has to be taken into account.
Within the scope of the manufacturing process, the contact parts can subsequently be adapted to the applicable requirements, and may be constructed as plug-type, soldered or other connections. In addition to the possibility of constructing these contacts later, it is also possible to construct them before the injection molding takes place around the components, for example, during the manufacturing of the stamping itself.
Another object of the present invention is to broaden the applicability of the process, and to create electronic control units which are constructed of various components and which are combined to a whole within the scope of different manufacturing processes. In this case, the mechanical loadability of the components is to be taken into account, and the mechanical and thermal load on the components is to be minimized during the manufacturing process.
In the multi-step manufacturing process of the electronic control unit (explained in detail by means of FIGS. 9 and beyond), a sequence of treatment operations is formed which, originating from the stamped grid as the mechanical basis, compensates the reduction of the mechanical stability which results from the stamped grid, by offsetting it with a simultaneous buildup of an alternative mechanical stability generated by a surrounding injection molding. This stability is based on the bodies made of a plastic material which are formed during first and second injection-molding-around operations. Together with the respective remaining portions of the stamped grid, these bodies provide sufficient stability of the control unit. At the same time, the molding-around operations achieve mechanical, thermal and chemical protection of components around which injection molding takes place; and the contacts between the components and the stamped grid structures are stabilized.
To achieve the above-mentioned objects, a duroplastic material is particularly suitable for the first molding-around operation and a thermoplastic material is particularly suitable for the second molding-around operation. Duroplastic materials are filled into a tool under pressure, and their molecular chains are interlinked at a higher temperature. These materials are known under commercial names, such as "NITTO 10-2" and are suitable for the direct sheathing of silicon semiconductors because of their minimal content of impurities, good thermal characteristics and good mechanical characteristics. However, the design possibilities are limited.
Thermoplastic materials, created by cooling a melting, are known under commercial names, such as "Hostalen". They are not suitable for the direct coating of semiconductors but, with a corresponding construction of the molds, can form complicated mechanical designs, such as housings with injection-molded-on plug collars.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.